Ct detector-module having radiation shielding for the processing circuitry

ABSTRACT

A CT detector-module-for detecting X-rays comprising: a matrix of photosensors, each of which generates signals responsive to photons incident thereon; a scintillator mounted over the matrix that converts X-rays incident on the scintillator to photons to which the photosensors are sensitive; an anti-scatter collimator mounted over the scintillator; and electronic circuitry located in close proximity to the photosensors to which each of the photosensors is connected for processing the signals generated by the photosensors; wherein parts of the module are formed from an absorbing material having a high X-ray absorption coefficient and shield the circuitry from radiation.

FIELD OF THE INVENTION

[0001] The present invention relates to computerized tomography (CT)X-ray imaging, and in particular to methods of shielding electronicsused to process signals generated by X-ray detectors in CT imagers.

BACKGROUND OF THE INVENTION

[0002] In CT X-ray imaging of a patient, X-rays are used to imageinternal structure and features of a region of the person's body. Theimaging is performed by a CT-imaging system, hereinafter referred to asa “CT-scanner” that images internal structure and features of aplurality of contiguous relatively thin planar slices of the body regionusing X-rays.

[0003] The CT-scanner generally comprises an X-ray source that providesa planar, fan-shaped X-ray beam and an array of closely spaced X-raydetectors that are substantially coplanar with the fan beam and face theX-ray source. The X-ray source and array of detectors are mounted in agantry so that a person being imaged with the CT-scanner, generallylying on an appropriate support couch, can be positioned within thegantry between the X-ray source and the array of detectors. The gantryand couch are moveable relative to each other so that the X-ray sourceand detector array can be positioned axially at desired locations alongthe patient's body.

[0004] The gantry comprises a stationary structure referred to as astator and a rotary element, referred to as a rotor, which is mounted tothe stator so that the rotor is rotatable about the axial direction. Inthird generation CT-scanners the X-ray source and detectors are mountedto the rotor. In fourth generation CT-scanners the detectors are mountedto the stator and form a non-rotating circular array. Angular positionof the rotor about the axial direction is controllable so that the X-raysource can be positioned at desired angles, referred to as “viewangles”, around the patient's body.

[0005] To image a slice in a region of a patient's body, the X-raysource is positioned at the axial position of the slice and the X-raysource is rotated around the slice to illuminate the slice with X-raysfrom a plurality of different view angles. At each view angle, detectorsin the array of detectors generate signals responsive to intensity ofX-rays from the source that pass through the slice. The signals areprocessed to determine amounts by which X-rays from the X-ray source areattenuated over various path lengths through the slice that the X-raystraverse in passing though the slice from the X-ray source to thedetectors. The amounts by which the X-rays are attenuated are used todetermine an X-ray absorption coefficient for material in the slice as afunction of position in the slice. The absorption coefficient is used togenerate an image of the slice and identify composition and density oftissue in the slice.

[0006] The X-ray detectors comprised in a detector array of CT-scannerare generally packaged in a plurality of modules, hereinafter referredto as “CT detector-modules”, each of which comprises a plurality ofX-ray detectors. Most modern CT-scanners are multi-slice CT-scannersdesigned to simultaneously image a plurality of slices of a patient. TheX-ray detectors in each CT detector-module of a multi-slice scanner arearranged in a rectangular matrix of rows and columns. The X-ray detectormatrices of any two CT detector-modules in a CT-scanner aresubstantially identical and comprise a same number of rows of detectorsand a same number of columns of detectors. The modules are positionedone adjacent to and contiguous with the other in a closely packed arraywith their rows of detectors aligned end to end so that the X-raydetectors form a plurality of long parallel rows of X-ray detectors. TheX-ray detectors in each long row of detectors lie on an arc of a circlehaving its center located substantially at a focal point of theCT-scanner's X-ray source.

[0007] A multi-slice scanner can theoretically be operated tosimultaneously image a number of slices of a patient up to a maximumnumber of slices equal to the number of rows of detectors. However,typically, signals from detectors in a multi-slice scanner are combinedin accordance with any of various algorithms known in the art tosimultaneously image a plurality of slices that is less than the numberof rows of detectors. Methods of combining signals from CTdetector-modules are described in U.S. Pat. Nos. 5,241,576 and 5,430,784and PCT publication WO 98/05980, the disclosures of which areincorporated herein by reference.

[0008] A prior art multi-slice CT-scanner may, by way of example,comprise 42 CT detector-modules each comprising 8 rows and 16 columns ofX-ray detectors. The multi-slice CT-scanner would then have 8 rows of672×-ray detectors. Typically, in operation signals from X-ray detectorsin two adjacent rows of detectors may be combined so that the CT-scannernormally operates to simultaneously image four slices of a patient.

[0009] Electronic components used to process signals from the X-raydetectors in a detector module are generally sensitive to radiation andif exposed to X-rays at intensities measured by the detectors arequickly damaged to an extent that causes them to become non-functional.As a result, electronic components for processing signals from the X-raydetectors in a CT detector-module are usually located at positionsremoved from the detector module for which intensities of X-rays fromthe X-ray source are relatively low. In addition, the electroniccomponents are shielded by appropriate radiation shielding. Eachdetector in a detector module is connected to the module's electronicprocessing components via a cable over which signals from the detectorare transmitted to the processing electronics.

[0010] To an extent to which CT detector-modules in a CT-scannercomprise a greater plurality of X-ray detectors and sizes of thedetectors decrease, resolution of the scanner can be increased andflexibility in configuring the CT-scanner for different imaging demandsis improved. However, as the number of X-ray detectors in a CTdetector-module increases, a required number of conductors in a cableconnecting the detectors to the processing electronics increases. Toaccommodate an increased number of conductors, size of the cable, and inparticular sizes of connectors that couple the cable to the CTdetector-module and to the processing unit increase. However, spaceavailable in a CT-scanner for a CT detector-module is limited and theimmediate neighborhood of each of the CT-modules in a CT-scanner iscrowded. As a result it does not appear feasible to provide requireddata transmission capacity using conventional cable for CTdetector-modules comprising a number of X-ray detectors substantiallylarger than a number of X-ray detectors typically comprised in prior artCT detector-modules.

[0011] A possible alternative to transmitting X-ray detector signals viacable to processing electronics is to locate the electronics in closeproximity to the detectors and connect the detectors to the electronicsusing electrical connections formed using known microfabricationtechniques. The processing electronics might, for example, be located ona same substrate as the detectors and/or on a different substrateconnected to the detector substrate using microconnectors known in theart. Known microfabrication materials and techniques can provide, inrestricted space available in a multi-slice CT-scanner, connectivitybetween processing circuits and X-ray detectors in the CT-scanner for asubstantially greater number of X-ray detectors than can be provided forby cable.

[0012] However, it may not have appeared feasible to locate processingelectronics for a CT detector-module in close proximity to the module'sX-ray detectors. The X-ray detectors in a CT detector-module are denselypacked and are closely coupled to a relatively large anti-scatteringcollimator. The CT detector-modules in a CT-scanner are also, as notedabove, closely packed one to the other and neighborhoods of the detectormodules are crowded. As a result, it may have appeared in prior art thatinsufficient space in the neighborhood of the X-ray detectors of a CTdetector-module is available to install radiation shielding sufficientto protect radiation sensitive electronic components located in closeproximity to the detectors.

SUMMARY OF THE INVENTION

[0013] An aspect of some embodiments of the present invention relates toproviding a CT detector-module comprising electronic components forprocessing signals generated by the module's detectors mounted in closeproximity to the detectors and having sufficient radiation shielding forprotecting the electronic components.

[0014] An aspect of some embodiments of the present invention relates toproviding a CT detector-module comprising a number of X-ray detectorssubstantially larger than a number of X-ray detectors generallycomprised in prior art CT detector-module

[0015] In accordance with an embodiment of the present invention, atleast some processing electronics for X-ray detectors comprised in a CTdetector-modules are mounted in close proximity to the X-ray detectorsoptionally on a same substrate as the detectors. In accordance with someembodiments of the present invention, the X-ray detectors are located ona first substrate and at least some signal processing electronics forthe detectors are optionally located on a second substrate. The twosubstrates are in close proximity to each other and are connectedtogether for transmission of signals between processing electronicsand/or X-ray detectors on the first substrate and processing electronicson the second substrate using one or more of a variety ofmicroconnectors or other suitable connections for transmission ofsignals.

[0016] According to an aspect of some embodiments of the presentinvention, shielding for the electronics mounted in close proximity tothe X-ray detectors of the CT detector-module is provided by formingparts of the module conventionally comprised in the module from amaterial having a suitably high X-ray absorption coefficient. Generally,parts of a CT detector-module must be machined to high tolerances. Theinventor has determined that materials suitable for forming precisionparts exist that also have a sufficiently high X-ray absorptioncoefficient so that parts of a CT detector-module formed from thematerials can provide effective radiation shielding to protectprocessing electronics mounted in close proximity to the module'sdetectors. By forming parts of a CT detector-module from suitableradiation absorbing shielding-material, sufficient radiation shieldingcan be packed into the limited space of a CT detector-module, inaccordance with an embodiment of the present invention, to protect theelectronic processing components. In some embodiments of the presentinvention, the parts, hereinafter referred to as “shielding parts”, ofthe CT detector-module formed from the shielding material compriseelements of an anti scattering collimator comprised in the module, whichis coupled to the X-ray detectors.

[0017] In some embodiments of the present invention, additionalstructural elements, hereinafter “supplementary shielding elements”, aremounted in the CT detector-module to provide radiation shielding for theelectronics, which is additional to shielding provided by the module'sshielding parts. The inventor has found that the supplementary shieldingelements can be designed so that they are accommodated in the limitedspace available for the CT detector-modules.

[0018] In accordance with embodiments of the present invention,connections between the X-ray detectors and processing electronics areprovided by connectors formed using microfabrication techniques.

[0019] By locating processing electronics for a CT detector-module inclose proximity to X-ray detectors in the module, on a same substrate onwhich the X-ray detectors are located or on a substrate closely adjacentto the X-ray detector substrate, connectors for connecting the X-raydetectors to the electronics can be conveniently fabricated usingmicrofabrication techniques. In the limited space available in a CTdetector-module and in a neighborhood of a CT detector-module comprisedin a CT-scanner, a substantially larger number of X-ray detectors can beconnected to processing electronics using microfabricated conductorsthan can generally be connected to processing electronics using cablesas in prior art. As a result, a CT detector-module in accordance with anembodiment of the present invention can comprise substantially more andsmaller X-ray detectors than are typically comprised in a prior art CTdetector-module. A CT-scanner comprising CT detector-modules inaccordance with an embodiment of the present invention, may thereforeprovide images of higher resolution than is typically provided by aprior art CT-scanner.

[0020] There is therefore provided, in accordance with an embodiment ofthe present invention, a CT detector-module for detecting X-rayscomprising: a matrix of photosensors, each of which generates signalsresponsive to photons incident thereon; a scintillator mounted over thematrix that converts X-rays incident on the scintillator to photons towhich the photosensors are sensitive; an anti-scatter collimator mountedover the scintillator; and electronic circuitry located in closeproximity to the photosensors to which each of the photosensors isconnected for processing the signals generated by the photosensors;wherein parts of the module are formed from an absorbing material havinga high X-ray absorption coefficient and shield the circuitry fromradiation.

[0021] Optionally, the absorbing material has an absorption coefficientfor X-rays that is larger than about 35 cm⁻¹. Optionally, the absorbingmaterial has an absorption coefficient for X-rays that is larger thanabout 40 cm⁻¹. Optionally, the absorbing material has an absorptioncoefficient for X-rays is equal to about 43 cm⁻¹.

[0022] In some embodiments of the present invention, the matrix isformed on a first planar substrate.

[0023] In some embodiments of the present invention, the collimatorcomprises an array of parallel anti scatter plates that aresubstantially perpendicular to the substrate and which are supported bytwo legs that are formed from the absorbing material.

[0024] In some embodiments of the present invention, a portion of atleast one of the legs shields at least a portion of the processingcircuitry.

[0025] In some embodiments of the present invention, each of the legshas an upright section perpendicular to the substrate and a foot havinga region substantially parallel to and in close proximity to the firstsubstrate. Optionally, the thickness of the foot region is greater thanabout 1.75 mm. Optionally, the thickness of the foot region is about 2mm.

[0026] In some embodiments of the present invention, the circuitrycomprises circuitry located on the first substrate and wherein a normalprojection of the foot region of at least one of the legs onto the firstsubstrate covers a region of the first substrate on which the circuitryis located. Optionally, a normal projection of the foot region of eachleg onto the first substrate covers a different region of the substrateon which the circuitry on the first substrate is located. Optionally,circuitry on the region of the first substrate covered by the normalprojection of the foot region of a leg is located between the footregion and the substrate.

[0027] In some embodiments of the-present invention, the circuitrycomprises circuitry located on a second planar substrate positioned inclose proximity to the first substrate. Optionally, the first and secondsubstrates are parallel and the first substrate is located between thesecond substrate and the scintillator.

[0028] In some embodiments of the present invention, a normal projectionof the foot region of at least one of the legs onto the second substratefalls on a region of the second substrate on which circuitry on thesecond substrate is located. Optionally, a normal projection of the footregion of each of the legs onto the second substrate covers a differentregion of the substrate on which circuitry on the second substrate islocated.

[0029] In some embodiments of the present invention, the CTdetector-module comprises at least one shielding body formed from anabsorbing material having a high X-ray absorption coefficient mountedbetween the first and second substrates so that a normal projection of aportion of the body onto the second substrate falls on a region of thesecond substrate on which circuitry on the second substrate is located.Optionally, the at least one shielding body comprises two shieldingbodies and wherein a projection of a portion of each of the bodies ontothe second substrate falls on a different region of the second substrateon which circuitry on the second substrate is located.

[0030] In some embodiments of the present invention, the projection ofthe portion of least one of the shielding bodies and the projection ofthe portion of a foot region of one of the legs on the second substratefall on a same region of the second substrate on which circuitry on thesecond substrate is located.

[0031] Optionally, the portion of the shielding body projected onto thesecond substrate has a thickness along the direction of projection thatis greater than about 1 mm. Optionally, the portion of the shieldingbody projected onto the second substrate has a thickness along thedirection of projection that is about 1.5 mm.

[0032] In some embodiments of the present invention, the circuitry onthe first substrate comprises at least one switching network thatreceives signals at each of a plurality of input ports and routesreceived signals to different ones of a plurality of output ports andwherein each photosensor is connected to an input of a switching networkof the at least one switching network.

[0033] In some embodiments of the present invention, the circuitry onthe second substrate comprises at least one processor for processingsignals generated by photosensors comprised in the matrix and each ofthe outputs of a switching network is electrically connected to at leastone processor of the at least one processor.

[0034] Optionally, the at least one processor amplifies photosensorsignals that it receives. Additionally or alternatively, the at leastone processor digitizes signals that it receives. In some embodiments ofthe present invention, the at least one processor determines the log ofattenuation of X-rays reaching a photosensor from an X-ray source in aCT-scanner comprising the CT detector-module, responsive to signals thatthe processor receives from the photosensor.

[0035] In some embodiments of the present invention, the matrixcomprises at least 256 photosensors. Optionally, the matrix comprises 16rows and 12 columns of photosensors.

[0036] In some embodiments of the present invention, the matrixcomprises at least 512 photosensors. Optionally, the matrix comprises 16rows and 24 columns of photosensors.

[0037] In some embodiments of the present invention, a dimension of thematrix parallel to the rows is less than about 2.5 cm.

[0038] In some embodiments of the present invention, parts of the moduleformed from an absorbing material are formed by injection molding theabsorbing material.

[0039] There is further provided, a CT-scanner comprising a CTdetector-module according to an embodiment of the present invention.

BRIEF DESCRIPTION OF FIGURES

[0040] Non-limiting examples of embodiments of the present invention aredescribed below with reference to figures attached hereto and listedbelow. In the figures, identical structures, elements or parts thatappear in more than one figure are generally labeled with a same numeralin all the figures in which they appear. Dimensions of components andfeatures shown in the figures are chosen for convenience and clarity ofpresentation and are not necessarily shown to scale.

[0041]FIG. 1 schematically shows a conventional CT-scanner, inaccordance with prior art;

[0042]FIGS. 2A and 2B schematically show an exploded perspective view ofa CT detector-module and a cross-sectional non-exploded view of the CTdetector-module respectively, in accordance with prior art;

[0043]FIG. 3 schematically show an exploded, perspective view of a CTdetector-module, in accordance with an embodiment of the presentinvention; and

[0044]FIG. 4 schematically shows a cross-sectional non-exploded view ofthe CT detector-module shown in FIG. 3, in accordance with an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0045]FIG. 1 schematically shows a third generation CT-scanner 20, inaccordance with prior art. Only those features and components ofCT-scanner 20 germane to the present discussion are shown in FIG. 1.

[0046] CT-scanner 20 comprises an X-ray source 22 controllable toprovide an X-ray fan-beam 24, schematically indicated by dashed lines26, and an array 28 of CT detector-modules 30 located opposite the X-raysource. Each CT detector-module 30 comprises a plurality of X-raydetectors (schematically shown in FIG. 2A but not shown in FIG. 1) forsensing intensity of X-rays in fan beam 24. Signals generated by theX-ray detectors in a detector module 30 responsive to X-rays incident onthe detectors are transmitted via a cable 32 to a processing unit 34that comprises electronic components (not shown) for processing thesignals.

[0047] X-ray source 22 and CT detector-modules 30 are mounted to a rotor40, which in turn is rotatably mounted to a stator 42 so that the rotorcan be rotated about an axis 44. Processing units 34 are also mounted torotor 40, generally in an array 36 parallel to array 28 and located on afar side of array 28 from X-ray source 22. A sheet 38 of shieldingmaterial, such as lead, located between array 28 and array 36 protectselectronic components in processing units 30 from damaging radiation.Stator 42 and rotor 40 are components of a gantry 46 of CT-scanner 20.

[0048] A patient to be imaged by CT-scanner 20 is supported on a couch48. Couch 48 is mounted on a suitable pedestal (not shown) and iscontrollable to be translated axially along axis 44 so as to position aregion of the patient's-body to be imaged by CT-scanner 20 inside gantry46, between X-ray source 22 and array 28. When the region to be imagedis properly positioned inside gantry 46, rotor 40 is controlled torotate X-ray source 22 around axis 44 to illuminate the region withX-rays from a plurality of view angles. For each view angle, analogsignals generated by the X-ray detectors in CT detector-modules 30responsive to X-rays from X-ray source 22 that pass through the regionare transmitted to processing units 34 via cables 32. In processingunits 34 the signals are generally amplified, digitized and formattedfor transmission to a suitable computer (not shown), which processes thedigitized signals it receives to generate an image of the region.

[0049] Each X-ray detector in a CT detector-module 30 is connected toprocessing electronics in processing unit 34 by a different conductor(not shown) in cable 32 that connects the CT detector-module to theprocessing unit. Maximum possible sizes of cable 32 and connectors (notshown) used to connect the cable to CT detector-module 30 and processingunit 34 are generally determined by spatial constraints in CT-scanner20. A number of conductors in cable 32 is in turn limited to a maximumnumber determined by the maximum sizes of cable 32 and/or its associatedconnectors. The maximum number of conductors sets an upper limit to anumber of X-ray detectors that can be comprised in CT detector-module30, if as in CT-scanner 20 and similar prior art CT-scanners, signalsgenerated by all the X-ray detectors in the module are transmitted viacable 32 to processing unit 34.

[0050]FIGS. 2A and 2B schematically show an exploded, perspective viewof a CT detector-module 30 comprised in CT-scanner 20 and a perspectiveview of the assembled CT detector-module respectively, in accordancewith the prior art. Some features and components of CT detector-module30 shown in the exploded view in FIG. 2A are not normally seen andtherefore are not shown in the perspective of the assembled view of themodule shown in FIG. 2B.

[0051] CT-module 30 comprises a rectangular matrix 50 of rows 52 andcolumns 54 of photosensors 56, such as photodiodes, mounted to anappropriate substrate 58. A plate 60, hereinafter “scintillator 60”,formed from an appropriate scintillation material for converting X-raysto photons to which the photosensors are sensitive, is sandwichedbetween photosensor matrix 50 and anti scatter collimator 62.

[0052] The number of photosensor rows 52 and the number of photosensorcolumns 54 shown in matrix 50 are chosen for convenience of presentationand are not necessarily equal to a number of rows and a number ofcolumns comprised in a particular prior art CT-scanner. Furthermore,whereas photosensors 56 in photosensor matrix 50 are shown as all beingsquare and having a same size and shape, in some CT detector-modules,photosensors in different rows 52 of matrix 50 have different sizes.Photosensors are also not necessarily square and photosensors may berectangular as well and a same CT detector-module may comprisephotosensors that are square as well as photosensors that arerectangular. A typical prior art CT detector-module may comprise eightrows 52 and sixteen columns 54 of photosensors 56. CT detector-modules30 are positioned in array 28 of CT-scanner 20 shown in FIG. 1, oneadjacent to and contiguous with the other, with their respectivephotosensor rows 52 aligned end to end and their respective collimators62 facing X-ray source 22.

[0053] Each photosensor 56 on substrate 58 is connected by a conductingelement (not shown) in or on substrate 58 to a connector 64 located atan end of the substrate. Connector 64 is used to connect CTdetector-module 30 to cable 32, shown in FIG. 1 and partially shown inFIG. 2A, that connects the CT-module to its corresponding processingunit 34. Cable 32 has a connector 66 that couples to connector 64 onsubstrate 58.

[0054] Collimator 62 comprises a pair of legs 71 supporting a pluralityof thin parallel anti scatter plates 70 formed from a heavy metal thathas a large absorption cross-section for photons. Plates 70 areseparated from each other by a distance that is equal to a width of acolumn 54 of photosensors to a high degree of accuracy. A number ofplates 70 in collimator 62 is equal to one more than a number of columns54 in photosensor matrix 56. Collimator 62 is mounted to substrate 58with plates 70 parallel to photosensor columns 54 and each plate 70accurately aligned with an edge of a column 54.

[0055] Collimator 62 and substrate 58 are usually formed with a suitableset of matching mounting holes 72 through which bolts and/or pins areinserted to mount collimator 62 to substrate 58. Scintillator 60 isbonded to substrate 58 and matrix 50 using an optical glue.

[0056] During operation of CT-scanner 20 to image a region of a patient,X-rays from X-ray source 22 (FIG. 1) that are incident on CTdetector-module 30 are converted to photons in scintillator 60, whichare sensed by photosensors 56. Each photosensor 56 generates an analogcurrent signal responsive to intensity of photons incident thereon. Thesignals are amplified and digitized in processor unit 34 (FIG. 1), whichthen transmits the digitized signals to a suitable computer. In somecases, circuitry in processing unit 34 uses the signals to determine thelog of attenuation of X-rays reaching CT detector-module 30 in a solidangle determined by the size of the photosensor 56 and its locationrelative to the X-ray aperture of X-ray source 22. In these cases thelog of the determined attenuation is transmitted to the computer. Thecomputer processes the digital signals it receives to generate an imageof the region.

[0057]FIGS. 3 and 4 schematically show an exploded, perspective view ofa CT detector-module 80 and a cross-sectional non-exploded view of theCT detector-module respectively, in accordance with an embodiment of thepresent invention.

[0058] CT detector-module 80 comprises a collimator 82, a scintillator84 and a rectangular matrix 86 of photosensors 88 mounted on a topsurface 89 of a substrate 90. Collimator 82 comprises a pair of legs 81supporting a plurality of anti scatter plates 83. Each leg 81 has anupright section 92 and a foot 94 formed with mounting holes 96. Eachphotosensor 88 is optionally connected by a conductor (not shown)formed, optionally using microfabrication techniques known in the art,in or on substrate 90 to one of two switching networks 98 mounted on thetop surface 89 of the substrate. Each switching network 98 is connectedby bus lines (not shown) in substrate 90 to a microconnector 100optionally located on a bottom surface 91 of substrate 90. Eachswitching network 98 routes analog signals that it receives fromphotosensors 88 to which it is connected to microconnector 100 via thebus lines connecting the switching network to the micro connector.

[0059] Substrate 90 is connected to a substrate 102 by means of amicroconnector 104 mounted on a top surface 101 of substrate 102 thatmatches microconnector 100 on substrate 90. Matching microconnector 104is connected to processors 106 optionally mounted on surface 101 ofsubstrate 102 and to processors 108 optionally mounted on a bottomsurface 103 of the substrate via conductors (not shown) formed in or onthe substrate. By way of example, microconnector 104 is connected tofour processors 106 located on top surface 101 and four processors 108mounted on a bottom surface 103 of the substrate. Each processor 108 islocated on bottom surface 103 directly “under” a processor 106 locatedon surface 101. Processors 108 are not shown in FIG. 3. Two processors108 are shown in the cross section view of CT detector-module 80 shownin FIG. 4.

[0060] Signals from photosensors 88 on substrate 90 that are routed byswitching networks 98 to microconnector 100 are transmitted to matchingconnector 104 on substrate 102. Each signal transmitted to matchingconnector 104 is forwarded from the matching connector to at least oneof processors 106 and 108 via a conductor or conductors (not shown)connecting the matching connector to the at least one of processors 106and 108. Processors 106 and 108 optionally amplify and digitize thesignals they receive and further process the signals as might berequired. The signals processed by processors 106 and 108 aretransmitted after processing to a microconnector 110 optionally mountedon bottom surface 103 of substrate 102. From microconnector 110 theprocessed signals are transmitted by cable (not shown) to a suitablecomputer, which generates images from signals that it receives.

[0061] It is noted that an amount of data transmitted by processors 106and 108 is substantially less than an amount of data that is generatedand transmitted by photosensors 88. In addition data transmitted byprocessors 106 and 108 is digital data, which is generally substantiallyless susceptible to corruption by noise than are the analog signalsgenerated by photosensors 88. Cables and connectors used to transferdata transmitted by processors 106 and 108 therefore do not generallyrequire as much shielding as do cables and connectors used to transferanalog data. As a result microconnector 110 and its associated cable cangenerally be substantially smaller than a microconnector and associatedcable that would be required to transmit data from photosensors 88 toprocessing circuitry were the photosensors connected to the processingcircuitry via a cable as in prior art.

[0062] Because switching networks 98 and processors 106 and 108 aremounted in close proximity to photosensors 88, intense X-ray radiationis directed substantially along a direction indicated by a block arrow120 towards the switching networks and processors when CTdetector-module 80 is in use in a CT-scanner. To provide radiationshielding for switching networks 98, processors 106 and processors 108,legs 81 of collimator 82 are formed, in accordance with an embodiment ofthe present invention, from a structural material having a highabsorption coefficient for X-rays and sufficient structural stability sothat the material can be used to form precision parts.

[0063] In accordance with an embodiment of the present invention, eachswitching network 98 on substrate 90 is located under a foot 96 of a leg81 so that a portion of the foot and upright section 92 of the leg arepositioned over the switching network. The locations of foot 94 andupright section 92 of a leg 81 relative to switching network 98 overwhich the leg is located is best seen in the cross-section view of CTdetector-module 80 shown in FIG. 4. In the cross section view uprightsection 92 and foot 94 are shown shaded. Portions of each leg 81therefore provide radiation shielding for a switching network 98.

[0064] Optionally a material from which legs 81 are formed has anabsorption coefficient greater than about 35 cm⁻¹. Optionally thematerial has an absorption coefficient greater than about 40 cm⁻¹.Optionally thickness of the region of foot 94 overlaying switchingnetwork 98 is greater than about 1.75 mm. The inventor has found that aTungsten Nylon composite marketed by Kanebo Ltd. of Japan under a tradename “NYLON MC102K13” is a suitable material for forming legs 81. Thematerial has a density of about 12 g/cm³, and an absorption coefficientfor X-rays of about 43 cm⁻¹ for X-ray energies of about 60 keV. Thematerial may conveniently be formed by injection molding to provide legs81. The material is also machinable and legs 81 can be formed bymachining the material as well. Using NYLON MC102K13 to form legs 71,the inventor has found that thickness of the region of foot 94 thatoverlays a switching network 98 is advantageously about 2 mm, whichthickness attenuates X-rays by well over 99.9%. Materialshaving-absorption coefficients for X-rays other than 43 cm⁻¹ may be usedin the practice of the present invention and use of such materials andcorresponding advantageous thickness for the region of foot 94overlaying switching network 98 made from such materials, will occur toa person of the art.

[0065] In addition, in accordance with an embodiment of the presentinvention, processors 106 and 108, which are located on substrate 102are positioned on the substrate so that each processor is also shieldedby a portion of foot 94 and upright section 92 of a leg 81. Additionalradiation shielding is optionally provided for processors 106 and 108 byeach of two supplementary shielding elements 112. Each supplementaryshielding element 112 is positioned between substrates 90 and 102 sothat a portion of the shielding element lies over a pair of processors106 and the pair of processor 108 directly under the pair of processors106. The location of each shielding element 112 relative to processors106 and 108 that it overlies is best seen in FIG. 4. In FIG. 4supplementary shielding elements are shown shaded. Supplementaryshielding elements 112 are optionally formed from a same material usedto form legs 81. For supplementary shielding elements 112 formed fromNYLON MC102K13 thickness of the portion of an element 112 that overlaysprocessors 106 is advantageously about 1.5 mm.

[0066] Supplementary shielding elements 112 and substrates 90 and 102are preferably formed with mounting holes 114 that match mounting holes96 in feet 94 of collimator 81. Bolts and/or pins (not shown) areoptionally inserted through mounting holes 96 and 114 to assemblecollimator 82 and to align collimator 81 substrates 90 and 102 andsupplementary shielding elements 112.

[0067] The inventor has determined that by forming legs 81 of collimator82 and providing the CT detector-module 30 with supplementary shieldingelements 112, in accordance with an embodiment of the present invention,effective radiation shielding is provided for switching networks 98 andprocessors 106 and 108.

[0068] By locating processing electronics, such as optionally switchingnetworks 98 and processors 106 and 108, for photosensors 88 in closeproximity to the photosensors, in accordance with an embodiment of thepresent invention, connectivity between the photosensors and theprocessing electronics is readily provided by conductors formed usingknown microfabricating techniques. As a result, a substantially largernumber of photosensors 88 can be connected to processing electronicsthan would generally be possible if the photosensors were connected toprocessing electronics using cables as in prior art. CT detector-module80, in accordance with an embodiment of the present invention, cantherefore comprise a substantially larger number of photosensors than isgenerally possible with prior art. “Microfabrication connectivity” in aCT detector-module, in accordance with an embodiment of the presentinvention also tends to make it easier to reduce the size ofphotosensors 88 and reduce costs of manufacture.

[0069] While the number and size of photosensors 88 shown in FIG. 3 isby way of example and chosen for convenience of presentation, theirnumber is greater than the number of photosensors 56 shown in FIG. 2Aand their size is smaller than photosensors 56. The number and size ofphotosensors 88 have been chosen to indicate that a CT detector-module,formed in accordance with an embodiment of the present invention, cancomprise more and smaller photosensors than photosensors generallycomprised in a prior art CT detector-module. For example, the inventorhas produced a CT detector-module in accordance with an embodiment ofthe present invention, similar to CT detector-module 80 comprising amatrix of photosensors having 24 rows and 16 columns of photosensors.The matrix is approximately 2.2 cm wide and about 5 cm long. Whereas thematrix has a same number of columns as the example of a prior art matrixnoted above, the matrix has three times as many rows as the prior artmatrix (which has only 8 rows of photosensors). A CT-scanner comprisingCT detector-modules in accordance with an embodiment of the presentinvention similar to CT detector-module 80 may therefore provide imagesof greater resolution than prior art CT-scanner and be more easilyconfigured to specific imaging demands.

[0070] In the description and claims of the present application, each ofthe verbs, “comprise” “include” and “have”, and conjugates thereof, areused to indicate that the object or objects of the verb are notnecessarily a complete listing of members, components, elements or partsof the subject or subjects of the verb.

[0071] The present invention has been described using detaileddescriptions of embodiments thereof that are provided by way of exampleand are not intended to limit the scope of the invention. The describedembodiments comprise different features, not all of which are requiredin all embodiments of the invention. Some embodiments of the presentinvention utilize only some of the features or possible combinations ofthe features. Variations of embodiments of the present invention thatare described and embodiments of the present invention comprisingdifferent combinations of features noted in the described embodimentswill occur to persons of the art. The scope of the invention is limitedonly by the following claims.

1. A CT detector-module for detecting X-rays comprising: a matrix of photosensors, each of which generates signals responsive to photons incident thereon; a scintillator mounted over the matrix that converts X-rays incident on the scintillator to photons to which the photosensors are sensitive; an anti-scatter collimator mounted over the scintillator; and electronic circuitry located in close proximity to the photosensors to which each of the photosensors is connected for processing the signals generated by the photosensors; wherein parts of the module are formed from an absorbing material having a high X-ray absorption coefficient and shield the circuitry from radiation.
 2. A CT detector-module according to claim 1 wherein the absorbing material has an absorption coefficient for X-rays that is larger than about 35 cm⁻¹.
 3. A CT detector-module according to claim 1 the absorbing material has an absorption coefficient for X-rays that is larger than about 40 cm⁻¹.
 4. A CT detector-module according to claim 1 the absorbing material has an absorption coefficient for X-rays is equal to about 43 cm⁻¹.
 5. A CT detector-module according to any of claims 1-4 wherein the matrix is formed on a first planar substrate.
 6. A CT detector-module according to claim 5 wherein the collimator comprises an array of parallel anti scatter plates that are substantially perpendicular to the substrate and which are supported by two legs that are formed from the absorbing material.
 7. A CT detector-module according to claim 6 wherein a portion of at least one of the legs shields at least a portion of the processing circuitry.
 8. A CT detector-module according to claim 7 wherein each of the legs has an upright section perpendicular to the substrate and a foot having a region substantially parallel to and in close proximity to the first substrate.
 9. A CT detector-module according to claim 8 wherein the thickness of the foot region is greater than about 1.75 mm
 10. A CT detector-module according to claim 8 wherein the thickness of the foot region is about 2 mm.
 11. A CT detector-module according to any of claims 8-10 wherein the circuitry comprises circuitry located on the first substrate and wherein a normal projection of the foot region of at least one of the legs onto the first substrate covers a region of the first substrate on which the circuitry is located.
 12. A CT detector-module according to claim 11 wherein a normal projection of the foot region of each leg onto the first substrate covers a different region of the substrate on which the circuitry on the first substrate is located.
 13. A CT detector-module according to claim 11 or claim 12 wherein circuitry on the region of the first substrate covered by the normal projection of the foot region of a leg is located between the foot region and the substrate.
 14. A CT detector-module according to any of claims 2-10 wherein the circuitry comprises circuitry located on a second planar substrate positioned in close proximity to the first substrate.
 15. A CT detector-module according to any of claims 11-14 wherein the circuitry comprises circuitry located on a second planar substrate positioned in close proximity to the first substrate.
 16. A CT detector-module according to claim 15 wherein the first and second substrates are parallel and the first substrate is located between the second substrate and the scintillator.
 17. A CT detector-module according to claim 16 wherein a normal projection of the foot region of at least one of the legs onto the second substrate falls on a region of the second substrate on which circuitry on the second substrate is located.
 18. A CT detector-module according to claim 16 wherein a normal projection of the foot region of each of the legs onto the second substrate covers a different region of the substrate on which circuitry on the second substrate is located.
 19. A CT detector-module according to any of claims 15-18 and comprising at least one shielding body formed from an absorbing material having a high X-ray absorption coefficient mounted between the first and second substrates so that a normal projection of a portion of the body onto the second substrate falls on a region of the second substrate on which circuitry on the second substrate is located.
 20. A CT detector-module according to claim 19 wherein the at least one shielding body comprises two shielding bodies and wherein a projection of a portion of each of the bodies onto the second substrate falls on a different region of the second substrate on which circuitry on the second substrate is located.
 21. A CT detector-module according to claim 19 or claim 20 wherein the projection of the portion of least one of the shielding bodies and the projection of the portion of a foot region of one of the legs on the second substrate fall on a same region of the second substrate on which circuitry on the second substrate is located.
 22. A CT detector-module according to any of claims 19-21 wherein the portion of the shielding body projected onto the second substrate has a thickness along the direction of projection that is greater than about 1 mm.
 23. A CT detector-module according to any of claims 19-21 wherein the portion of the shielding body projected onto the second substrate has a thickness along the direction of projection that is about 1.5 mm.
 24. A CT detector-module according to any of claims 15-23 wherein the circuitry on the first substrate comprises at least one switching network that receives signals at each of a plurality of input ports and routes received signals to different ones of a plurality of output ports and wherein each photosensor is connected to an input of a switching network of the at least one switching network.
 25. A CT detector-module according to claim 24 wherein the circuitry on the second substrate comprises at least one processor for processing signals generated by photosensors comprised in the matrix and each of the outputs of a switching network is electrically connected to at least one processor of the at least one processor.
 26. A CT detector-module according to claim 25 wherein the at least one processor amplifies photosensor signals that it receives.
 27. A CT detector-module according to claim 25 or claim 26 wherein the at least one processor digitizes signals that it receives.
 28. A CT detector-module according to any of claims 25-27 and wherein the at least one processor determines the log of attenuation of X-rays reaching a photosensor from an X-ray source in a CT-scanner comprising the CT detector-module, responsive to signals that the processor receives from the photosensor.
 29. A CT detector-module according to any of the preceding claims wherein the matrix comprises at least 256 photosensors.
 30. A CT detector-module according to claim 29 wherein the matrix comprises 16 rows and 12 columns of photosensors.
 31. A CT detector-module according to any claims 1-28 wherein the matrix comprises at least 512 photosensors.
 32. A CT detector-module according to claim 31 wherein the matrix comprises 16 rows and 24 columns of photosensors.
 33. A CT detector-module according to any of claims 29-32 wherein a dimension of the matrix parallel to the rows is less than about 2.5 cm.
 34. A CT detector-module according to any of the preceding claims wherein parts of the module formed from an absorbing material are formed by injection molding the absorbing material.
 35. A CT-scanner comprising a CT detector-module according to any of claims 1-33. 